Skew control apparatus for feeding a wide-web ribbon in a high speed printer

ABSTRACT

An apparatus and method for feeding a wide-web inking ribbon in alternate directions between a pair of mandrels in an on-the-fly printer. The mandrels are detachably mounted in the printer such that their positions may be interchanged and the locations of the ribbon&#39;&#39;s left and right portions reversed. This extends the ribbon&#39;&#39;s life when printing is performed only in columns grouped at one side of the document. The apparatus includes means for sensing and correcting skew in the ribbon as it travels between the two mandrels. A photoelectric sensor, positioned adjacent an edge of the ribbon, senses any skew and in response signals a tracking device which axially moves one of the mandrels to overcome the skew. The tracking device includes a movable shaft having a series of teeth thereon which mesh with the teeth of a gear rotatable in either direction by a reversible motor in response to the output of the sensor. Where the ribbon feed is used in a &#39;&#39;&#39;&#39;shuttle&#39;&#39;&#39;&#39; printer which prints each line by initially printing one group of columns and then &#39;&#39;&#39;&#39;shuttling&#39;&#39;&#39;&#39; the document to print another group of columns in the line, a pair of sensors are used. They cause the tracking device to move the mandrel so that the ribbon alternately tracks along two paths spaced apart a distance equal to the distance the document is shuttled. This allows substantially the entire area of the ribbon to be used. Even with the usual type of on-the-fly printer which prints in all the columns of a line at one time, the ribbon preferably tracks along two paths. In this case, the distance between the two paths is equal to one-half the distance between adjacent columns so that those areas of the ribbon which would normally always be located at the spaces between the columns are used.

United States Patent Lozeau et a1.

[54] SKEW CONTROL APPARATUS FOR FEEDING A WIDE-WEB RIBBON IN A HIGH SPEED PRINTER [72] Inventors: Paul R. Lozeau; Charles J. Sabonls, both of Utica, N.Y.

[73] Assignee: Mohawk Data Sciences Corporation,

l-lerkimer, NY.

[22] Filed: April 15, 1970 ['21] Appl. No.: 28,794

[52] US. Cl. ..101/336, 197/133, 197/151, 226/20 [51] Int. Cl. ..B41l 27/00 [58] Field of Search ..101/336, 352; 197/133, 134, 197/15l,157,158,159,160,161,162,163, 164,165,166,167,172,175, DIG. 10;

[5 6] References Cited Primary Examiner-Emest T. Wright, Jr. Attorney-Francis J. Thomas, Richard H. Smith,

Zinn and MacPeak [451 Oct. 31, 1972 [5 7 ABSTRACT An apparatus and method for feeding a wide-web inking ribbon in alternate directions between a pair of mandrels in an on-the-fly printer. The mandrels are detachably mounted in the printer such that their positions may be interchanged and the locations of the ribbons left and right portions reversed. This extends the ribbons life when printing is performed only in columns grouped at one side of the document. The apparatus includes means for sensing and correcting skew in the ribbon as it travels between the two mandrels. A photoelectric sensor, positioned adjacent an edge of the ribbon, senses any skew and in response signals a tracking device which axially moves one of the-mandrels to overcome the skew. The tracking device includes a movable shaft having a series of teeth thereon which mesh with the teeth of a gear rotatable in either direction by a reversible motor in response to the output of the sensor. Where the ribbon feed is used in a shuttle printer which prints each line by initially printing one group of columns and then shuttling the document to print another group of columns in the line, a pair of sensors are used. They cause the tracking device to move the mandrel so that the ribbon alternately tracks along two paths spaced apart a distance equal to the distance the document is shuttled. This allows substantially the entire area of the ribbon to be used. Even with the usual type of on -the-fly printer which prints 1n all the columns of a line at one time, the ribbon preferably tracks along two paths. In this case, the distance between the two paths is equal to one-half the distance between adjacent columns so that those areas of the ribbon which would normally always be located at the spaces between the columns are used.

4 Claims, 7 Drawing Figures CONTROL INVENTORS PAUL R. LOZEAU CHARLES J. SABONIS BY /%M (,5 4

ATTORNEY PATENTEDucI 31 me SHEET 2 BF 4 INVENTOR.

PATENTED I973 3.701.318

sum 3 or 4 INVENTOR.

SKEW CONTROL APPARATUS FOR FEEDING A WIDE-WEB RIBBON IN A HIGH SPEED PRINTER BACKGROUND OF THE INVENTION This invention relates to printing and, more particularly, to feeding a wide-web inking ribbon past the print line of an on-the-fly printer.

High speed on-the-fly printers have been developed to print the rapidly generated output information of data processing apparatus. In these printers, print hammers strike the document being printed upon and an inking ribbon against type characters on a type carrier (such as a drum or chain) moving at high speed in back of the document. Activation of the hammers is timed with respect to the movement of the type carrier such that selected type characters are impacted. The document being printed upon is successively advanced past the print line (i.e., the imaginary line at which characters are printed) after each line is printed to present another line to the hammers.

The inking ribbon for many of these printers is of the wide-web variety in which the ribbons width extends parallel to the print line and the ribbon is moved in its longitudinal direction past the print line to present different areas of the ribbon to the hammers. lt thereby provides a new supply of ink for each line. The ribbon is generally fed between a pair of mandrels in alternate directions. However, because of the ribbons large width, it has a tendency to deviate from a straight path or skew between the two mandrels. Since the ribbon must pass across all the columns to be printed at the print line and since the ribbon must remain unwrinkled, such skew is obviously a problem.

In many data processing applications, printing is only required in a group of columns at the beginning of each line. Of course, printing in this manner only utilizes the left portion of the wide-web ribbon. When the ink in this portion has been used, the ribbon is no longer useful for general applications and must usually be discarded even though the right portion of the ribbon still contains ink.

One particular type of on-the-fly printer is the shuttle printer as disclosed and claimed in U. 8. Pat No. 3,313,390 issued to R. H. Curtiss on April ll, 1967. In this printer, the moving type carrier (i.e., the type drum) presents type characters at the print line to a first group of columns in the line being printed. These columns are printed and then the document is moved or shuttled along the print line to present a second group of columns in the line being printed to the type characters on the carrier and these columns are printed. The type characters are presented to the document at alternate columns and the document is shuttled a distance equal to the width of one column; thus, each line is printed in two steps. Since printing occurs only at the alternate columns where the moving type-"carrier presents its type characters, the wide-web inking ribbon is only used at these locations. Those places on the ribbon which are not adjacent the type characters on the carrier are not used and some of the ribbon is wasted.

With the usual type of on-the-fly printer, type characters are simultaneously presented to all the columns in the line being printed. Thus, each portion of the wide-web ribbon at a column is used but those spaces between columns are not. Although less of the ribbon is wasted than with a shuttle printer, some of the ink on the ribbon is not utilized.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved ribbon feed for an on-the-fly printer which allows maximum use of a wide-web inking ribbon.

It is another object to provide such a ribbon feed which allows maximum use of the ribbon when printing is only performed in a group of columns at one side of the document being printed upon.

It is another object of this invention to provide a ribbon feed which allows maximum use of a wide-web inking ribbon in a shuttle printer.

It is a further object of this invention to provide a ribbon feed having improved means for overcoming skew in a wide-web inking ribbon in an on-the-fly printer.

According to the invention, a method and apparatus are provided for feeding a wide-web ribbon in an onthe-fly printer. The ribbon is fed in alternate directions between two mandrels detachably mounted in the printer so that their positions may be interchanged and the locations of the left and right portions of the ribbon reversed. When printing is only performed in the columns at one side of the document being printed upon (e.g., the beginning columns at the left of the document), the mandrels'positions are interchanged allowing the locations of the left and right portions of the ribbon to be reversed. This extends the ribbons life since it allows the previously unused portion of the ribbon to be utilized.

Means is provided for overcoming skew in the ribbon as it moves between the two mandrels. A tracking device, responsive to a sensor for ascertaining such skew, axially moves one of the mandrels to overcome the sensed skew. The tracking device comprises a movable shaft having an end at which an end of the mandrel is maintained by biasing means. The shaft has a series of spaced teeth extending along it which are adapted to mesh with the teeth of a gear rotatable in either direction by a reversible motor which is responsive to the sensor. To prevent unnecessary stress on the motor, a second spring is provided to counterbalance the force of the first spring.

With a shuttle" printer, two sensors are provided which are alternately used. Each of these senses an edge of the ribbon at a location such that the distance between the position of the ribbon when an edge is sensed by one sensor and the ribbons position when an edge is sensed by the other sensor is equal to the distance the document is shuttled along the print line. When either of the sensors sense an edge of the ribbon substantially no skew exists. Thus, by alternately utilizing the two sensors, the ribbon alternately tracks on two substantially skew-less paths. Since the distance between the two paths and the distance that the paper is shuttled is also the distance between the columns of type characters on the moving carrier, those areas of the inking ribbon which normally are not used with a shuttle printer are utilized.

, The invention also provides for maximum use of a wide-web inking ribbon in the usual type of on-the-fly printer which presents type characters to all the columns of each line without moving the document. As

with the shuttle printer, a pair of sensors are provided and the ribbon alternately tracks along two skew-less paths determined by the sensors. However, the distance between the sensors is substantially equal to one-half the distance between adjacent columns in the line. This arrangement utilizes those areas of the ribbon which would be located at spaces between the columns and not utilized if the ribbon tracked along only one path.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified isometric view of an on-the-fly drum printer adapted to utilize a preferred embodiment of the ribbon feed.

FIG. 2 is a front view, partially in section, of a preferred embodiment of the ribbon feed.

FIGS 3 and 4 are views taken along lines 3--3 and 4-4 in FIG 2.

FIG. 5 is a view showing the sensor assembly for ascertaining skew in the ribbon.

FIG. 6 is a simplified view illustrating the invention with a shuttle printer.

FIG. 7 is a logic diagram of a control circuit which may be used in practicing the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an on-the-fly printer having a print drum it 1 with type characters (not shown) on its periphery. The drum 1 is mounted on a shaft 2 and rotated at a constant speed by a motor 4. The document 3 being printed upon is stepped upwardly by a pair of schematically illustrated conventional paper feed tractors 5 which engage edge perforations 3a in the document 3. The document 3 is stepped after each line is printed so that the succeeding line may be printed. A bank of print hammers 7 is positioned adjacent the drum 1 and the document 3 passes between the bank of hammers 7 and drum 1. These hammers 7 may consist of any of the variety used in on-the-fly impact printing. When one of the hammers 7 is actuated if forces the document 3 and a wide-web inking ribbon 9 against a selected type character on the drum 1 which is to be printed. By firing a plurality of the hammers 7 a row of characters is printed in a print line extending across the document 3.

For ascertaining which type characters are approachingthe hammers 7 at each instant, a circular code disc 11 of conventional construction is mounted on shaft 2 and rotates with the drum 1. As is conventional, the code disc 11 contains radial rows of coded apertures 1 1a representing the characters onthe drum 1. Light from a light source 12 is passed through these apertures 11a in code disc to a photosensing device 14 which provides coded signals to the control circuits 16 controlling the printer. The characters to be printed are also represented by coded electrical signals fed to the control circuits 16 on data input line 18. These signals are compared with the signals from the and photosensing device, 14 and the hammers 7 are energized by the circuit 16 to print the type characters on the drum 1 which correspond to the input characters received on line 18.

The ribbon 9 is mounted on the yoke 13 of the printer. It is of the wide-web variety having its width extending parallel to and along the print line between the drum 1 and hammers 7. The ribbon 9 is alternately fed between an upper and a lower 9b roll so that it continually passes between the hammers 7 and drum 1. At the print line the ribbon 9 provides the ink necessary for the imprint when a hammer 7 impacts a type character on the drum 1. The ribbon 9 is fed past the print line to continually present new areas of the ribbon 9 to the hammers 7 and drum 1 so that successive lines may be imprinted with different areas of the ribbon 9. Since used areas of the ribbon 9 regain ink from unused areas by capillary action, the direction of ribbon movement is reversed and the ribbon 9 again travels across the print line. This feeding of the ribbon 9 in alternate directions continues until the ribbon 9 no longer has sufficient ink for printing.

Referring to FIG 2, the upper 9a and lower 9b rolls of ribbon 9 are wound on hollow cylindrical mandrels 15a and 15b mounted within the yoke 13 with each end of the ribbon 9 connected to one of the mandrels 15a or 15b. The opposite ends of each mandrel 15a or 15b are engaged by a pair of caps 17a, 17b and 170 and 17d. The caps 17a, 17b, 17c, 17d have annular tapering portions 19a 19b, 19c and 19d which fit within the ends of the mandrels 15a and 15b and circular flanges 21a 21b, 21c and 21d abutting the mandrels ends. The caps 17a and 17c engaging the right ends of the mandrels 15a and 15b include teeth 23a and 23b which engage in a pair of cooperating notches provided at the right ends of the mandrels 15a and 15b. The caps 17a and 170 are secured to a pair of shafts 25a and 25b, respectively. The shafts 25a and 2511 are adapted to be rotated by a driving means 27 which may include, for example, a conventional motor and gear train coupled to the shafts 25a and 25b and secured to the right side of yoke 13 with fasteners 29. With the cooperating notches at the right ends of the mandrels 15a and 15b allows the mandrels 15a and 15b to be drivingly engaged and rotated by the shafts 25a and 25b. The other caps 17b and 17d on the left side support the left ends of the mandrels 15a and 15b and rotate on a pair of shafts 31a and 31b.

Referring to the lower mandrel 15b shown in FIG 2, the shaft 31b is biased toward the mandrel 15b by a compression spring 33 which is located in a cavity at the left side of yoke 13. The spring 33 maintains the cap 17d against the left end of the lower mandrel 15b and biases the mandrel ISbagainst the cap 170 at its right end. Thus, the spring 33 maintains the lower mandrel 15b and the caps 17c and 17d in operative engagement with one another. However, the mandrel 15b may be detached and removed from the caps 17c and 17d by manually forcing shaft 31b to the left against the bias of spring 33.

Referring now to the upper mandrel 15a in FIG 2. its left cap 17b is rotatably mounted on shaft 31a in a manner similar to that in which cap 174 is mounted on shaft 31b. The upper mandrel may also be manually detached from the printer. However, this is accomplished in a different manner than with the lower mandrel 15b. The right cap 17a engaging the right end of the upper mandrel 15a has an elongated inner section 35 projecting from its tapered portion 19a into the interior of the upper mandrel 15a. This projecting inner section 35 is hollow and the end portion of shaft 25a slidably projects into it. At the end of shaft 25a another shaft 37 of smaller diameter is attached. This small diameter shaft 37 is located within the hollow inner section 35 and projects out the end 41 thereof which engages the small shaft 37 in a sliding fit. Between the small-diameter shaft 37 and the inner surface of the hollow inner section 35 a compression spring 39 is located. This spring 39 bears against the end of shaft 25a and the end 41 of inner section 35. It biases the cap 17a into engagement with the mandrel a and maintains the mandrel 15a in operating engagement with caps 17a and 17b. To detach the upper mandrel 15a it is manually moved to the right against the bias of spring 39 and away from its left cap 17b.

Since the cap 17a is slidable with respect to shaft 250 a finger 43 and groove 45 are provided to drivingly engage the two. The finger 43 is located on the inner surface of the caps hollow inner section 35 and slidably fits into the groove 45 which is provided in the shaft 25a. This allows the cap 17a at the right end of the upper mandrel 15a to be driven by the driving means 27 In many data processing applications, only those columns at the beginning of each line at the left side of the document 3 are printed. The invention allows the positions of the mandrels 15a and 15b to be interchanged such that the left and right portions of the ribbon 9 reverse their positions. Both mandrels 15a and 15b may be detached from the printer and the upper mandrel 15a engaged by those caps previously engaging the lower mandrel 15b and the lower mandrel 15b engaged by those caps previously engaging the upper mandrel 15a. During this procedure, the mandrels 15a and 15b are also turned around so that their left ends exchange positions with their right ends. Thus, the portion of the ribbon 9 previously on the left in FIG 2 becomes placed on the right. After interchanging their positions, the mandrels 15a and 15b are engaged by the caps 17a, 17b, 17c and 17d in he same manner as previously described. Note that notches 47 are placed at the left ends of the mandrels 15a and 15b shown in FIG 2 so that when the mandrels 15a and 15b are turned around they may be engaged by the teeth 23a and 23b on the right caps 17a and 17c. By thus interchanging the mandrels positions and reversing the left and right portions of the ribbon 9, the unused portion of the ribbon 9 previously on the right is now on the left. It may now be used for printing in the columns at the beginning of the lines being printed at the left of the document 3.

As previously disclosed, the ribbon 9 is fed onto one mandrel 15a or 15b and then reversed and wound on the other mandrel 15a or 15b by the action of driving means 27. This process of ribbon feeding in alternate directions continues during printing operations. Numerous methods and apparatus are known for reversing the direction of ribbon feed and the specific apparatus employed is not relevant to an understanding of the present invention. For example, the apparatus shown and described in U.S. Pat No. 3,266,745 issued to W.Y. Benson on Aug. 16, 1966 may be employed to drive and reverse the ribbon. The driving means 27 shown in FIG. 2 of the instant specification may be constructed as illustrated by the arrangement of motor 36 drive shafts 6 and 8 and the interconnecting drive elements including the clutches 16-20-42 and 14-18-40 and relay 82 as shown in FIG. 1 of the cited patent.

As seen in FIG 1, the left portion of the yoke 13 has mounted thereon an assembly 147 for sensing the edge of the ribbon 9 as it moves between the mandrels 15a and 15b. The assembly 147 is shown in FIG 5 and comprises a pair of photodiodes D1 and D2 (schematically illustrated) which are set within a plastic case 51. The case 51 has a slot 51a within which the left edge of the ribbon 9 rides. Aligned with the photodiodes D1 and D2 are a pair of light elements L1 and L2 (schematically illustrated), each of which is adapted to direct light onto an aligned photodiode D1 or D2. Light passes from the light elements L1 and L2 through he slot 51a onto the associated photodiodes'Dl and D2. The latter provide, an electrical signal indicative of the position of the ribbon 9.

The sensing assembly 147 is provided to sense skew in the ribbon 9 as it moves between the two mandrels 15a and 15b. Only one photodiode D1 or D2 is utilized to sense ribbon skew at a particular time. When skew occurs, the photodiode D1 or D2 being utilized will either be energized by light passing through the slot 51a thus producing an electrical signal of a first level indicating that the ribbon 9 is too far to the right, or the photodiode D1 or D2 will receive substantially no light and will reproduce signal of a second level indicating that the ribbon 9 is too far to the left. Thus, the photodiode D1 or D2 senses whether the ribbon 9 is skewed by ascertaining the location of the ribbons left edge.

In response to the photodiode D1 or D2, the upper mandrel 15a is positioned axially to correct and overcome existing skew. The state of the photodiode D1 or D2 (covered by the ribbon or exposed to the light) determines the direction the upper mandrel 15a should be moved. If the ribbon 9, as sensed by the photodiode D1 or D2, is skewed to the left, the upper mandrel 15a is moved to the left to overcome the skew. Conversely, the upper mandrel 15a is moved to the right to overcome skew causing the edge of the ribbon 9 to be to the right of the photodiode D1 or D2. The tracking device for axially moving the upper mandrel 15a in this manner in response to the photodiode D1 or D2 is shown in FIGS 2, 3, and 4.

Referring to these Figures, the left end of shaft 310 is mounted within a housing member 55 secured to the left part of the yoke 13. The shaft 31a is slidably supported within housing 55 by a pair of bushings 57a and 57b, At its right end, the shaft 31a rotatably supports the cap 17b as previously described. Also as previously disclosed, the cap 17a engaging the right end of the upper mandrel 15a is biased toward the upper mandrel 15a by a spring 39 and thus forces the upper mandrel 15a toward the left so that its left end engages the left cap 17b. When the shaft 31a is moved, it will displace the upper mandrel 15a axially. This is done in response to signals from one of the photodiodes D1 and D2 previously described in connection with FIG 5.

To move the shaft 31a, a series of equally spaced teeth 59 are mounted on the shaft 31a and extend along it. The teeth 59 are engaged by the teeth of a gear 61 mounted on the shaft 63 of a reversible motor 65. The motor 65 is attached to the housing 55 by an angle bar 67 and fasteners 69 allowing the motor 65 to be suspended from the yoke 13. The motor 65 moves the shaft 31a in either axial direction in response to the output signal generated by one of the photodiodes D.

When the gear 61 reaches approximately either end of the series of teeth 59, one of a pair of micro-switches 71a and 71b is closed to stop the motor 65 before the gear 61 runs out of the teeth 59. The contact of each of these micro-switches 71a and 71b is depressed by an angle bracket 73 mounted on the top of shaft 31a. The micro-switch 71a or 71b then activates appropriate electrical circuitry to stop both the motor 65 and the printing operation as well. For one of the microswitches 71a and 71b to be closed by angle 73 the ribbon 9 must have become wound on the mandrels 15a and 15b in an extremely irregular manner. After the printing operation has been automatically stopped the ribbon 9 is manually rewound so that it may track in a skew-less path.

As shown in FIGS 2 and 3, to accommodate the micro-switches 71a and 71b, bracket 73 and the motor shaft 63-, appropriate cavities 75a and 75b are located within housing 55.

As previously noted, the motor 65 is adapted to move shaft 31a both with and against the bias of spring 39. Spring 39 continually forces the upper mandrel 15a and shaft 31a toward the left. This force can cause unnecessary stresses in the motor 65. To overcome this force, another spring 76 is provided at the left end of the housing 55 to bias the shaft 31a toward the right. The spring 76 is chosen so that it substantially nullifies and counterbalances the force from spring 39.

As seen in FIGS 2 and 4, one end of the spring 76 bears against the shaft 31a within a recess 77 located at the shafts left end. The other end of the spring 76 bears against the inside surface of a hollow member 79 which is mounted on the left end of housing 55 with fasteners 81. The member 79 comprises an annular portion 80 which is closed and shaped at its left end (as seen in FIG 2) to maintain the left end of the spring 76 in place. Fasteners 81 secure the hollow member 79 to housing 55 by projecting through a circular flange 82 integral with the annular portion 80 of hollow member 79. A cover plate 83 is provided around housing 55 for protecting the tracking assembly.

FIG. 6 illustrates the operation of a shuttle printer and a method for feeding a ribbon 209 according to the invention in such a printer is shown and described in detail in U.S. Pat. No. 3,313,390 issued to R.H. Curtiss on April 11, 1967. The rotating type drum 200 in the shuttle printer schematically illustrated in FIG 6 has spaced fonts 201 located at alternate columns of the line to be printed on the document 203. During a printing operation, the columns on the document 203 which are aligned with the fonts 201 are printed; the position of the document 203 at this time is indicated at the letter in FIG. 6. After these columns are printed the document 203 is shuttled or moved along the print line in the direction of the arrow designated b. This is accomplished by moving the paper feed tractors (FIG. 1) laterally. The document 203 is stopped at the position indicated by the letter 0 so that those columns originally located at the spaces between the fonts 201 are now aligned with them. Printing is then performed in these columns and the entire line is complete. The ribbon 209 is alternately fed between two mandrels such as 150 and b, FIG. 2 in the directions shown by the arrow designated c.

However, the ribbon 209 on alternate passes is shifted along the print line in the directions of the arrow designated e. This is accomplished by alternate use of the photodiodes D1 and D2 mounted adjacent an edge of the ribbon 209, in the manner shown in FIG. 5 and discussed above. As previously noted, only one photodiode D1 or D2 is used for ribbon tracking at a time. When one photodiode D1 or D2 is used, the ribbon 209 will track along one path; when the other photodiode D1 or D2 is being utilized, the ribbon 209 tracks upon a different path. The difference between these two paths, determined by the distance between photodiodes D1 and D2, is equal to one half the distance between the fonts 201 on the print drum 200 which, of course, is the distance the document 203 is shuttled between a and c. Therefore, spaced portions of the ribbon 209 will be utilized when tracking in conjunction with one photodiode D1 or D2 and other spaced portions of the ribbon 209 will be used when tracking by the other photodiode D1 or D2. This allows twice as much ribbon 209 to be used than would be if the ribbon 209 tracked along only one path. Of course, as previously noted, either photodiode D1 or D2 causes the ribbon 209 to track on a substantially skew-less path.

The ribbon 209 may be made to track along two paths with the usual type of on-the-fly printer to achieve maximum ribbon use. With this type of printer, type characters are simultaneously presented to all the columns in the line being printed and the type characters on the drum 1 are not spaced as shown with the shuttle printer in FIG. 6. The ribbon feed of the invention operates in the same manner as just previously described in reference to the shuttle printer. However, the photodiodes, D1 and D2, (and their aligned light elements L1 and L2) are spaced apart a distance equal to one-half the center-to-center distance between adjacent columns. This causes the ribbon 209 to track along two paths spaced apart by this distance and utilizes the ink in the ribbon 209 normally contained in the space between columns when the ribbon 209 tracks along only one path.

FIG. 7 is a schematic logic diagram of a control circuit which may be used with the ribbon feed of the invention. The elements of diagram operate in a conventional manner on a binary voltage level basis wherein the inputs to the elements and the outputs therefrom always exist at either of two discreet voltage levels the positive voltage level or the negative voltage level of the system.

The outputs of photodiodes D1 and D2 are fed to a circuit 84 for selecting which of these outputs is to be used for ribbon tracking. As previously noted, only one of the photodiodes D1 or D2 are used at a time. The photodiodes outputs are suitably amplified by amplifiers 85a and 85b and fed to AND gates 87 and 89. AND gates 87 and 89 are well known circuit elements which provide a positive output voltage only when all input lines exist at the positive level. The control and choice of photodiodes D1 and D2 is effected by a switch means such as a flip-flop 91 acting in conjunction with the AND gates 87 and 89. The flip-flop 91 is a well known bistable logic circuit element. Each positive signal at its T input causes its 1 output to go positive and stay positive while simultaneously its 0 output goes negative and stays negative (assuming that the 1 output was initially negative and the 0 output initially positive). Conversely, a succeeding positive signal at its T input will cause its 1 output to go negative and stay negative while simultaneously its output goes positive and stays positive. The outputs of flip-flop 91 are each connected to one of the AND gates 87 or 89 as conditioning inputs. Thus, only one of the AND gates 87 or 89 will pass the amplified output of a photodiode D1 or D2 at a particular time (the particular AND gate 87 or 89 depending on which output of flip-flop 91 is positive).

Successive inputs to flip-flop determines which of the photodiodes, D1 or D2 is utilized. Such an input signal may be derived from a ribbon reverse apparatus such as those previously referred to in which an electrical signal is provided each time the ribbon 9 (FIG. 1) becomes essentially completely wound on one'of the mandrels a and 15b. For example, such a signal may be derived with suitable impedance buffering and amplification from the circuit of relay winding 86 shown in FIG. 1 of the previously cited Pat No. 3,266,745. This signal may be used to trigger and change the state of flip-flop 91. However, preferably the flip-flop 91 is triggered by a signal from the ribbon reverse apparatus only when the ribbon 9 becomes essentially all wound on the upper mandrel 15a. In any case, the state of the flip-flop 91 is periodically changed to thereby alternately use the outputs from photodiodes D1 and D2. Each time the photodiodes D1 or D2 being utilized is changed in this manner, the tracking assembly moves the upper mandrel 1521 (FIG. 2) and ribbon 9 so that the ribbon 9 tracks on a different path.

The outputs of both AND gates 89 and 87 are fed to an OR gate 93. The OR gate 93 is another well known logic circuit element. It provides a positive level output only when one or more of its input lines is at the positive level. The output of OR gate 93 provides the output signal from the photodiode selecting circuit 84.

This output is fed to a tracking circuit 95 for moving the shaft 31a shown in FIG 2. As previously noted, the shaft 31a is moved by a reversible motor 65. The motor 65 has two inputs which operate to drive it and move the shaft 31a in either direction. Because the motor 65 is being controlled by a logic circuit, a pair of driving circuits 97 and 99 are required at the motors inputs. The voltage levels used in logic circuits are relatively low and the driving circuits 97 and 99 are required to connect the low output of the logic elements to a sufficiently high voltage to control the motor 65.

The output from the photodiode selecting circuit 84, fed to the tracking circuit 95, operates one of the driving circuits 97 or 99 to move the shaft 31a via motor 65 in one of its two axial directions. An inverter 101 is provided between the input to the tracking circuit 95 and the driver 97. The input to the tracking circuit 95 is applied directly to the other driver 99.

The inverter 101 provides an output level which is always opposite to its input level. Thus, if a positive voltage is fed to the tracking circuit 95 it activates driver 99 to drive the motor 65 so that shaft 31a is moved in one direction, i.e., to the right. The positive voltage will not activate driver 97 because inverter 101 will convert the positive voltage to a negative one. Conversely, if a negative voltage is applied to the tracking circuit 95, driver 99 will not be activated. However, this negative voltage will be applied to driver 97 as a positive voltage due to the inverter 101. Driver 97 will thus drive motor 65 to cause it to move the shaft 31a in the other direction, i.e., to the left.

Whether a positive or negative voltage is applied to the tracing circuit depends on whether the photodiode D1 or D2 being used for tracking is active or inactive. As shown in FIG 5, the photodiode D1 or D2 associated with the path then being tracked by the ribbon 9 will be active and generate a first level signal for the tracking circuit 95 when the ribbon 9 is too far to the right at the sensor assembly 147. This first level signal causes the motor 65 to move the shaft 31a to the right whereby the ribbon will be shifted to the left. Conversely, if the ribbon 9 is too far to the left, the photodiode D1 or D2 will be inactive and a second level signal will be applied to the tracking circuit 95. This causes the motor 65 to move the shaft 31a to the left whereupon the ribbon 9 shifts to the right.

FIG. 7 also shows a simplified logic circuit 102 by which each of the micro-switches 71a or 71 shuts off motor 65 and the printer itself when contacted by the angle bracket 73 shown in FIG 2. Either of the microswitches 71a or 71b when closed, applies a positive voltage to activate a single shot circuit 103. The single shot circuit 102 is another well known circuit element; it generates a negative to positive to negative square wave output pulse of fixed duration in response to a negative to positive transition at its input. The output pulse of single shot 103 is fed to the printers electronic controls schematically illustrated as block 16in FIG. 1. This shuts off the printer. The output of single shot 103 is also fed as an input to another driving circuit for shutting off the motor 65. Thus, when gear 61 mounted on the shaft 63 of motor 65 (FIG. 2) reaches an end of the series of teeth 59 and one of the micro-switches 71a or 71b is closed, the motor 65 is shut off and the printing operation is stopped.

OPERATION The operation of the ribbon feed of the invention will now be briefly described.

Assuming that photodiode D1 is being used initially with the 1 output of flip-flop 91 (FIG. 7) beingpositive, the ribbon tracking circuit 95 for controlling the motor 65 will respond to the state of photodiode D1. The photodiode D1 is mounted adjacent the left edge of the ribbon (FIG. 5) as it moves between the mandrels 15a and 15b. When the ribbon 9 is moving in a path such that it has substantially no skew, the left edge of the ribbon 9 is located directly at the photodiode D1 as shown in FIG 5. If photodiode D1 is receiving sufficient light from source L1 to be activated, the resultant first level output signal from the photodiode D1 causes motor 65 to drive mandrel 15a to the right whereupon the ribbon 9 is shifted to the left. This eventually causes the light to be blocked from photodiode D1 and the resultant second level signal therefrom reverses the direction of motor 65 and the ribbon 9 begins shifting to the right. The end effect is a hunting" of the left edge of the ribbon 9 back and forth across the face of photodiode Dl as the ribbon 9 feeds past the print line.

In similar fashion, the left edge of the ribbon 9, when being fed in the opposite direction, hunts across the face of photodiode D2 and thus tracks along a path of?- set from the path established, in the manner just v discussed, by photodiode D1. The average distance of the offset between the two tracking paths is equal to the distance between the centers of photodiodes D1 and D2.

Therefore, in addition to providing positive skew control in both ribbon 9 feed directions, the present invention achieves a more complete utilization of the ribbon 9, with resultant increase in ribbon life, in printing systems, such as the shuttle printing system described above briefly and in more detail in the above cited US. Pat No. 3,313,390, wherein characters are distributed across the print line in a non-contiguous or spaced-apart configuration.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. In a printer for printing characters in a print line wherein the gap between each pair of adjacent character positions in said line is greater than the width of a character and wherein ink for said printing is supplied by an inked web mounted on a pair of rotatable mandrels constructed and arranged to feed said web in alternate feed cycles longitudinally past said print line first in one direction perpendicular to said line and then in the opposite direction, means for controlling the feeding of said web comprising, in combination:

mandrel positioning means for varying the position of one of said mandrels to shift said web in either direction lateral to its path of movement past said print line; first sensing means positioned adjacent an edge of said web for sensing changes in the lateral position I thereof and generating a first output signal indicative of said changes; second sensing means also positioned adjacent said edge of said web and spaced from said first sensing means in a direction parallel to said print line by a distance equal to half the distance between adjacent character positions in said print line, said second sensing means adapted to sense changes in the lateral position of said web edge and to generate a second output signal indicative of said changes; v control means responsive either to said first output signal or to said second output signal for operating said mandrel positioning means to maintain said web in substantiaily a fixed lateral position with respect to said first sensing means or said second sensing means as said web feeds past said print line;

switch means operable in either a first state for supplying said first output signal to said control means or in a second state for supplying said second output signal to said control means; and

means for reversing the state of said switch means coincident with the initiation of each alternate web feed cycle whereby printing is effected from one portion of said web during the feeding of said web in said one direction and from another portion of said web during feedin in said opposite direction. 2. The combination set orth in claim 1 wherein said mandrel positioning means comprises means for shifting said one of said mandrels in either direction along its axis.

3. The combination set forth in claim 2 wherein said first and second sensing means comprise:

a support member positioned adjacent said web such that an edge portion of said web passes over said member;

first and second photodiodes affixed to said support member in the area of said web edge, said photodiodes being spaced apart from one another in the direction of said print line by a distance equal to half the distance between adjacent character positions in said print line;

means for illuminating said photodiodes; and

circuit means connected to said photodiodes for generating said first and second output signals in response to the coaction of said web edge with said first and second photodiodes, respectively, each of said first and second output signals being generated at a first level when said web covers the associated photodiode and being generated at a second level when the associated photodiode is exposed to said illuminating means.

4. The combination set forth in claim 3 wherein said control means comprises bidirectional motor means constructed and arranged to shift said one mandrel in a first direction in response to said first level of said first or said one second output signals and to shift said mandrel in the opposite direction in response to said second level of said first or said second output signals whereby said web is continually shifted laterally back and forth with said web edge positioned over either said first or said second photodiode.

l l t t 

1. In a printer for printing characters in a print line wherein the gap between each pair of adjacent character positions in said line is greater than the width of a character and wherein ink for said printing is supplied by an inked web mounted on a pair of rotatable mandrels constructed and arranged to feed said web in alternate feed cycles longitudinally past said print line first in one direction perpendicular to said line and then in the opposite direction, means for controlling the feeding of said web comprising, in combination: mandrel positioning means for varying the position of one of said mandrels to shift said web in either direction lateral to its path of movement past said print line; first sensing means positioned adjacent an edge of said web for sensing changes in the lateral position thereof and generating a first output signal indicative of said changes; second sensing means also positioned adjacent said edge of said web and spaced from said first sensing means in a direction parallel to said print line by a distance equal to half the distanCe between adjacent character positions in said print line, said second sensing means adapted to sense changes in the lateral position of said web edge and to generate a second output signal indicative of said changes; control means responsive either to said first output signal or to said second output signal for operating said mandrel positioning means to maintain said web in substantially a fixed lateral position with respect to said first sensing means or said second sensing means as said web feeds past said print line; switch means operable in either a first state for supplying said first output signal to said control means or in a second state for supplying said second output signal to said control means; and means for reversing the state of said switch means coincident with the initiation of each alternate web feed cycle whereby printing is effected from one portion of said web during the feeding of said web in said one direction and from another portion of said web during feeding in said opposite direction.
 2. The combination set forth in claim 1 wherein said mandrel positioning means comprises means for shifting said one of said mandrels in either direction along its axis.
 3. The combination set forth in claim 2 wherein said first and second sensing means comprise: a support member positioned adjacent said web such that an edge portion of said web passes over said member; first and second photodiodes affixed to said support member in the area of said web edge, said photodiodes being spaced apart from one another in the direction of said print line by a distance equal to half the distance between adjacent character positions in said print line; means for illuminating said photodiodes; and circuit means connected to said photodiodes for generating said first and second output signals in response to the coaction of said web edge with said first and second photodiodes, respectively, each of said first and second output signals being generated at a first level when said web covers the associated photodiode and being generated at a second level when the associated photodiode is exposed to said illuminating means.
 4. The combination set forth in claim 3 wherein said control means comprises bidirectional motor means constructed and arranged to shift said one mandrel in a first direction in response to said first level of said first or said one second output signals and to shift said mandrel in the opposite direction in response to said second level of said first or said second output signals whereby said web is continually shifted laterally back and forth with said web edge positioned over either said first or said second photodiode. 